U.S. Pat. No. 3,840,508 (Ballard) discloses a process for polymerizing olefinically unsaturated monomers using as an initiator a reaction product of a transition metal complex and a matrix material which has a hydroxylated surface but which is otherwise substantially inert.
U.S. Pat. No. 4,228,263 (Howard) discloses a catalytic process for preparing elastomeric polymers of propylene. The catalyst, which is a reaction product of a metal oxide and an organometallic compound of the formula (RCH.sub.2).sub.4 M wherein M is Zr, Ti, or Hf, and R is aryl, aralkyl, tertiary alkyl, or trialkylsilyl, is prepared in situ in a solvent consisting principally of liquid propylene; the solvent may also contain volatile materials, such as hexane, which are used to introduce the catalyst components. A similar process for preparing elastomeric polypropylene is disclosed in British Specification 2,001,080 (Collette).
U.S. Pat. No. 3,932,307 (Setterquist) discloses a process for polymerizing 1-olefins using a catalyst system based on the reaction product obtained by contacting a solution of tetra(neophyl)zirconium in a hydrocarbon medium, with a hydroxylated oxide of a metal of Group IIa, IIIa, IVa, or IVb of the Periodic Table of the Elements. Fumed alumina, i.e., alumina prepared by burning aluminum chloride in the presence of water vapor, is an exemplified preferred metal oxide and provides an especially active catalyst system. Related catalyst systems and polymerization processes are disclosed in U.S. Pat. Nos. 3,950,269 (Setterquist); 3,971,767 (Setterquist); 4,011,383 (Setterquist); and 4,304,685 (Howard).
In U.S. Pat. No. 4,335,225 (Collette et al.), these types of catalyst systems, which are the reaction product of an organometallic compound with the partially hydrated surface of a metal oxide, are used to polymerize propylene to a novel elastomeric polypropylene. In addition to tetra(neophyl)zirconium, other specified types of organometallic derivatives of Group IVa transition metals, i.e., titanium, zirconium, and hafnium, are described as being suitable catalyst components. The polypropylene polymerization may be carried out by a solution method, in which the propylene is present as a solution in an inert hydrocarbon such as cyclohexane. Alternatively, polymerization may be carried out by a slurry method, wherein the polymerization medium is essentially excess liquid propylene, and only a relatively minor amount of an inert hydrocarbon solvent, from the catalyst suspension, is present. The slurry method is preferred. Hydrogen may be present to control molecular weight. The preferred catalyst in U.S. Pat. No. 4,335,225 is produced from reactions employing tetra(neophyl)zirconium (TNZ), which is disclosed in U.S. Pat. No. 4,017,525 (Setterquist).
Tetra(hydrocarbyl)metallic compounds, such as (TNZ), are usually isolated as solid materials. It is known in this art that these catalyst precursor organometallic compounds in solid form are reasonably stable as such if protected from oxygen and water, and are even more stable if they are also stored below room temperature at about 20.degree. C. or lower. However, if they are not so protected, or if stored in solvents such as n-alkanes, isoalkanes, and aromatics, they are known to decompose with formation of hydrocarbons, colored soluble organometallic compounds, and deeply-colored insoluble organometallic compounds. The composition of the colored species is unknown. Decomposition products of TNZ are tert-butylbenzene and highly-colored (yellow, brown, or black) organometallic compounds. The decomposition products form in detectable amounts within hours or days at room temperature. The formation and precipitation of these organometallic decomposition products leads to deterioration and variability in the activity of the catalysts prepared therefrom.
It would be of great commercial advantage if a solvent, in which these tetra(hydrocarbyl)metallic compounds were stable, were available. This would facilitate the manufacture, storage, and transportation of these compounds, i.e., the solid would not have to be isolated during production, and the solution environment would not have to be kept below 20.degree. C. during containment and storage. It would be even more advantageous if said tetra(hydrocarbyl)metallic compounds in such a stabilizing solvent could be converted to the active catalyst for subsequent use in, e.g., olefin polymerization, without having to re-isolate the solid material and add another hydrocarbon solvent.
The present invention provides a process to achieve a chemically stable composition of organometallic catalyst precursor compounds in solution form. Costs of refrigeration in storing and transporting the catalyst precursor can then be reduced or eliminated; improved convenience in handling is achieved; and uniformity in the activity of the resulting activated catalyst can be realized. The present invention also provides a composition comprising organometallic catalyst precursors in solution form, which can be used directly to make activated catalysts, thereby providing a significant improvement in the catalyst preparation process.
Applicants have found that the compositions of the present invention are stable for much longer periods of time than those in the solvents used previously; and have further found that the compositions of the present invention can be added directly to the catalyst preparation process, i.e., the olefins of the composition do not inhibit formation of an activated catalyst. These results were unexpected in light of the prior art, and the fact that the activated catalysts derived from the compositions of this invention are normally used for olefin polymerization. Even more unexpected was the fact that the activated olefin polymerization catalysts could be formed in the presence of the olefins of the present invention without any loss in catalytic activity.